Parsoid/JS had a lib/mw/Batcher.js that batched MediaWiki API requests and so, AddMediaInfo's serialized requests would get batched before they went out on the network.
However, Parsoid/PHP does not have a backend batcher. The requests go through one of the DataAccess layers.
Since Parsoid/PHP is synchronous code, this batching ability has to be built into AddMediaInfo by restructure that code to issue requests in batches and process results after all batches are processed.
**Caveat**: By batching imageinfo requests, we may potentially defeat DB query caching. So, this needs to be done carefully with appropriate research / evaluation.
Additionally, we should also deduplicate requests for the same image -- this is especially an issue on pages that use a lot of icons (flags, yes/no checkmarks images, etc.) in tables.